Function parse_pixel_value_or_system 

pub fn parse_pixel_value_or_system(
    input: &str,
) -> Result<PixelValueOrSystem, CssPixelValueParseError<'_>>

Parse a pixel value that may include system metric references.

Accepts: 10px, 1.5em, system:button-padding, etc.

Errors

Returns an error if input is not a valid CSS pixel-value-or-system value.